Semiconductor light emitting device

ABSTRACT

A resonant cavity type light emitting diode has a first DBR made of n-type AlAs or Al 0.5 Ga 0.5 As, a quantum well active layer, a second DBR made of p-type (Al 0.2 Ga 0.6 ) 0.5 In 0.5 P or Al 0.5 In 0.5 P, and an n-type current constriction layer on an n-type GaAs substrate. The first DBR and the second DBR form a resonator. The quantum well active layer is formed in a position of an antinode of a standing wave inside the resonator. Between the second DBR and the current constriction layer, there is provided a p-type GaP etching protection layer that has a value obtained by dividing resistivity by thickness being 1×10 3  Ω or more. Since a current in a current flow pass formed in the current constriction layer hardly diffuses to the outside of the current flow pass, there is generated few region with low current density that causes deterioration of responsespeed in a quantum well layer. Thus, the light emitting diode has an excellent high-speed response.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor light emitting device.

In recent years, srmironrlrtcor light emitting devices have been widelyused for information indication panels, optical communications and thelike. These semiconductor light emitting devices are not only requiredto have high light emitting-efficiency, but also a high-speed responsewhen they are used for optical communications in particular. Therefore,speed semiconductor light emitting devices having higher efficiency andquicker response are being vigorously developed.

A surface emitting type LED (Light Emitting Diode) allowing low currentoperation is drawing attention as a semiconductor light emitting devicehaving high efficiency. However, the surface emitting type LED isrelatively insufficient in high-speed response. The data transmissionspeed of the surface emitting type LED is at best around 100 Mbps to 200Mbps. Consequently, a resonant cavity type LED has been developed. Inthe resonant cavity type LED, a light emission layer is located on anantinode of a standing wave formed by a resonator composed of twomirrors. Thereby, spontaneously emitted light is controlled to achievehigh-speed response and high efficiency of the light emitting element(refer to Japanese Patent Laid-Open Publication HEI No. 3-229480 andU.S. Pat. No. 5,226,053). Recently, POF (Plastic Optical Fiber) has beenused for high-speed communication system conforming to IEEE1394, USB2and the like. As a preferable light source of POF, there has beendeveloped a resonant cavity type LED in which AlGaInP basedsemiconductor material is used for its light emission layer. This LEDenables high-efficient light emittance at a wavelength of 650 nm that isincluded in a low loss wavelength range in the POF (High BrightnessVisible Resonant Cavity Light Emitting Diode: IEEE PHOTONICS TECHNOLOGYLETTERS VOL.10 NO.12 DECEMBER 1998).

However, the resonant cavity type LED having the AlGaInP based lightemission layer has a problem in moisture resistance. The problem iscaused by layers of AlAs and AlGaAs whose Al mix crystal ratio is closeto 1 in the vicinity of the LED surface, as a result of using amultilayered reflection film made of AlGaAs based material as a mirrorfor forming a resonator. Also, the above-stated resonant cavity type LEDhas another problem that an optical output saturates when a current flowof several tens mA or more is applied. This problem is caused byinsufficient diffusion of current because current applied from a surfaceof the LED diffuses only in DBR (Distributed Bragg Reflector) havingapprox. 1 μm thickness. For solving these problems, there has beenproposed an idea of forming a surface electrode into the shape of ahoneycomb or mesh with a width of several μm. However, such electrodehas a drawback that breakage of the electrode is easily generated, whichcauses degraded reliability of LED.

Under these circumstances, there has been proposed a semiconductor lightemitting device whose multilayered reflection film is composed ofAlGaInP based materials, where the multilayered reflection film isformed on the surface side of the semiconductor light emitting device toconstitute a resonator (refer to Japanese Patent Laid-Open PublicationNo. 2001-68732). This semiconductor light emitting device not onlyincreases moisture resistance owing to the AlGaInP based materials whichthe multilayered reflection film of the device is made of, but alsoincreases density of current applied onto a light emission layer owingto a current constriction layer. Further, a current diffusion layer isprovided to solve the problem of optical output saturation.

In the above-stated conventional semiconductor light emitting device,however, current diffuses toward outside of a current flow pass formedby the current constriction layer. Thereby, the diffused current causesa low-current-density region to generate in the light emission layer.The low-current-density region is low in response speed, which causes aproblem that the response speed of the entire device is decreased.

SUMMARY OF THE INVENTION

An object of the invention is to provide a semiconductor light emittingdevice having good high-speed response.

To achieve the object, the present invention provides a semiconductorlight emitting device comprising:

a semiconductor substrate;

a first multilayered reflection film on the semiconductor substrate;

a light emission layer on the first multilayered reflection film;

a second multilayered reflection film made of Al_(y)Ga_(z)In_(1-y-z)P(O≦y≦1, 0≦z≦1) on the light emission layer;

a semiconductor layer on the second multilayered reflection film; and

a current constriction layer on the semiconductor layer,

wherein the first multilayered reflection film and the secondmultilayered reflection film form a resonator with a specified interval,and the light emission layer is formed in a position of an antinode of astanding wave inside the resonator, and

wherein the semiconductor layer has a value obtained by dividingresistivity by thickness being 1×10³ Ω or more.

Since the semiconductor layer has relatively large resistivity andrelatively small carrier density, a current in a current flow passformed in the current constriction layer will not easily diffuse to theoutside of the current flow pass. Therefore, there is generated fewregion with low current density in the light emission layer, whicheffectively improves a response characteristic of the semiconductorlight emitting device.

Herein, when the semiconductor layer between the second multilayeredreflection film and the current constriction layer has a value smallerthan 1×10³ Ω obtained by dividing resistivity by thickness, an amount ofcurrent diffused to the outside of the current flow pass formed by thecurrent constriction layer becomes so large as to pose bad influence tothe response characteristic of the semiconductor light emitting device.

Conventionally, in the surface emitting type semiconductor lightemitting device without resonator structure, a layer between the lightemission layer and the current constriction layer was set to have acarrier density of approx. 3×10¹⁸ cm⁻³ for reducing series resistance.In such semiconductor light emitting device, it was not recognized thatthe carrier density of the layer between the light emission layer andthe current constriction layer hindered increase of response speed. Aninventor of the present invention has found out that the cause ofcurrent diffusion from the current flow pass formed in the currentconstriction layer correlates with the resistivity of the layer betweenthe multilayered reflection film formed on the light emission layer andthe current constriction layer, and has invented the present inventionbased thereon.

It is noted that throughout the specification, y and z in semiconductorcompounds are independent in each semiconductor compound.

The present invention also provides a semiconductor light emittingdevice comprising:

a semiconductor substrate;

a first multilayered reflection film on the semiconductor substrate;

a light emission layer on the first multilayered reflection film;

a second multilayered reflection film made of Al_(y)Ga_(z)In_(1-y-z)P(O≦y≦1, 0≦z≦1) on the light emission layer; and

a current constriction layer on the second multilayered reflection film,

wherein the first multilayered reflection film and the secondmultilayered reflection film form a resonator with a specified interval,and the light emission layer is formed in a position of an antinode of astanding wave inside the resonator, and

wherein a percentage of a current diffused to an outside of a currentflow pass formed in the current constriction layer is 25% or less of atotal current applied to the current flow pass.

Since the current diffused to the outside of the current flow pass is25% or less of the total current applied to the current flow pass, it ispossible to reduce the region with low current density in the lightemission layer to the extent that bad influence is not given to theresponse characteristic of the entire semiconductor light emittingdevice. On the contrary, if the percentage of the current diffused tothe outside of the current flow pass formed in the current constrictionlayer is beyond 25% of the total applied current, the regions with lowcurrent density due to the current diffused to the outside of thecurrent flow pass become excessive, which deteriorates the responsecharacteristic of the entire semiconductor light emitting device.

In one embodiment of the present invention, the semiconductor lightemitting device further comprises a current diffusion layer on thecurrent constriction layer.

Acccrding to the above embodiment, the current applied from the surfaceof the semiconductor light emitting device is uniformly led by thecurrent diffusion layer to the current flow pass formed in the currentconstriction layer. Therefore, it becomes possible to effectively reduceoperating voltage of the semiconductor light emitting device.

In one embodiment of the present invention, the light emission layer ismade of Al_(y)Ga₂In_(1-y-z)P (O≦y≦1, 0 ≦z≦1). According to the aboveembodiment, it becomes possible to obtain emitted light at a wavelengthrange from 550 nm to 680 nm.

In one embodiment of the pregsent invention, a semiconductor layer madeof Al_(y)Ga_(z)In_(1-y-z)P (O≦y≦1, 0≦z ≦1) is provided between thesecond multilayered reflection film and the current constriction layer.

Therefore, the semiconductor layer becomes transparent against the lightwith a wavelength of 550 nm or more, which enables highly effectiveextraction of emitted light with a wavelength of 550 nm or more.

In one embodiment of the present invention, a semiconductor layer madeof GaP is provided between the second multilayered reflection film andthe current constriction layer. The surface of this semiconductor layeris hardly oxidized, which makes it possible to grow a semiconductorlayer with good crystallinity on top of this layer. As a result, itbecomes possible to obtain a semiconductor light emitting device withless lattice mismatch and crystal defect and with good characteristics.

In one embodiment of the present invention, the current constrictionlayer is made of Al_(y)Ga_(z)In_(1-y-z)P (O≦y≦1, 0≦z≦1). Consequently,the current constriction layer becomes transparent against the lightwith a wavelength of 550 nm or more, which enables highly effectiveextraction of emitted light with a wavelength of 550 nm or more.

In one embodiment of the present invention, the current constrictionlayer is made of GaP. The surface of this semiconductor layer ishardlyoxidized, which makes it possible to grow a semiconductor layer withgood crystallinity on top of this layer. As a result, it becomespossible to obtain a semiconductor light emitting device with lesslattice mismatch and crystal defect and with good light-emittingcharacteristics.

In one embodiment of the present invention, the current diffusion layeris made of A_(y)Ga_(z)In_(1-y-z)P (O≦y≦1, 0≦z≦1). Consequently, thecurrent diffusion layer becomes transparent against the light with awavelength of 550 nm or more, which enables highly effective extractionof emitted light with a wavelength of 550 nm or more.

Also, the semiconductor substrate is preferably made from GaAs inconsideration of crystallinity of a semiconductor layer formed thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1A is a plane view showing a semiconductor light emitting device ina first embodiment of the present invention, while FIG. 1B is a crosssectional view taken along line A—A of FIG. 1A;

FIG. 2 is a cross sectional view showing the state of the semiconductorlight emitting device of FIGS. 1A and 1B in a manufacturing process;

FIG. 3A is a plane view showing the state of the semiconductor lightemitting device in a manufacturing process different from that of FIG.2, while FIG. 3B is a cross sectional view taken along line B—B of FIG.3A;

FIG. 4 is a view showing change of a current diffused to the outside ofa current flow pass when resistivity of an etching protection layer 9 ischanged;

FIG. 5 is a view showing change of rise time of the semiconductor lightemitting device when resistivity of an etching protection layer 9 ischanged;

FIG. 6A is a plane view showing a semiconductor light emitting device ina second embodiment, while FIG. 6B is a cross sectional view taken alongline C—C of FIG. 6A;

FIG. 7 is a cross sectional view showing the state of the semiconductorlight emitting device of FIGS. 6A and 6B in a manufacturing process; and

FIG. 8A is a plane view showing the state of the manufacturing processof the semiconductor light emitting device different from that of FIG.7, while FIG. 8B is a cross sectional view taken along line D—D of FIG.8A.

DETAIDED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, the present invention will be described in detail inconjunction with embodiments with reference to the drawings.

FIG. 1A is a plane view showing a semiconductor light emitting device ina first embodiment of the present invention. FIG. 1B is a crosssectional view taken along line A—A of FIG. 1A. FIG. 2 is a crosssectional view showing a state of the semiconductor light emittingdevice of FIGS. 1A and 1B in a manufacturing process. FIG. 3A is a planeview showing a state of the semiconductor light emitting device in amanufacturing process different from the manufacturing process shown inFIG. 2. FIG. 3B is a cross sectional view taken along line B—B of FIG.3A.

The semiconductor light emitting device of the present embodiment is anAlGaInP based semiconductor light emitting device. First, on an n-typeGaAs substrate 1 as a semiconductor substrate inclined 15° in [011]direction from (100) plane, there are laminated in sequence by MOCVD(Metal Organic Chemical Vapor Deposition) method an n-type Gas bufferlayer 2 (layer thickness of lpi, and carrier density of 5×10¹⁷ cm⁻³), asshown in FIG. 2, an n-type first DBR (Distributed Bragg Reflector) 3(carrier density of 5×10¹⁷ cm⁻³) as a first multilayered reflectionfilm, an n-type (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P first cladding layer 4(carrier density of 5×10¹⁷ cm⁻³), a quantum well active layer 5 as alight emission layer, a p-type (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P secondcladding layer 6 (carrier density of 5×10¹⁷ cm⁻³), a second DBR 7(carrier density of 5×10¹⁷ cm⁻³) as a second multilayered reflectionfilm, a p-type AlGaInP intermediate layer 8 (layer thickness of 0.1 μm,and carrier density of 5 ×10¹⁸ cm⁻³), a p-type GaP etching protectionlayer 9 (layer thickness of 1 μm, and carrier density of 1×10¹⁸ cm⁻³),an n-type GaP layer 10 (layer thickness of 0.3 μm, and carrier densityof 3×10¹⁸ cm⁻³), and an undope GaAs cap layer 11 (layer thickness of0.01 μm).

The first DBR 3 is formed by 30.5 pairs of n-type AlAs and n-typeAl_(0.5)Ga_(0.5)As. The quantum well active layer 5 is formed by a GaInPwell layer and an Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P barrier layer. Thesecond DBR 7 is formed by 12 pairs of p-typeAl_(0.2)Ga_(0.8))_(0.5)In_(0.5)P and p-type Al_(0.5)In_(0.5)P.

Herein, the n-type first DBR 3 and the p-type second DBR 7 are formedsuch that a center of reflectance spectrum is 650 nm. An intervalbetween the DBRs 3 and 7, that is, a resonator length is adjusted sothat a resonance wavelength of a resonator composed of these two DBRs 3,7 becomes 650 nm. In the present embodiment, the resonator length is setto be equal to two wavelengths. Further, the quantum well active layer 5is formed so as to position at an antinode of a standing wave generatedin the resonator composed of the above two DBRs 3, 7, and to have anemission peak wavelength of 650 nm.

The n-type GaAs cap layer 11 is then removed with sulfuric acid/hydrogenperoxide etchant. Thereafter, part of the n-type GaP layer 10 is etchedoff till the p-type GaP etching protection layer 9 is exposed by usingphoto lithography and sulfuric acid/hydrogen peroxide etchant. As shownin FIGS. 3A and 3B, this etching process forms a circular opening of 70μm in diameter, which functions as a current flow pass, so as to formthe n-type GaP current constriction layer 10.

After that, a p-type AlGaInP current diffusion layer 12 is laminated onthe p-type etching protection layer 9 and the n-type currentconstriction layer 10, as shown in FIG. 1. The p-type AlGaInP currentdiffusion layer 12 is formed such that a total layer thickness is 7 μm Alower 1 μm-thick portion of the layer 12 has a carrier density of 1×10¹⁸cm⁻³ while an upper 6 μm-thick portion of the layer 12 has a carrierdensity of 1×10¹⁹ cm⁻³. Then, on the p-type current diffusion layer 12,AuBe/Au is deposited. The deposited AuBe/Au is etched by photolithography and Au echant and then heat-treated to obtain a p-typeelectrode 13. Meanwhile, a back face of the GaAs substrate 1 is polishedto have a thickness of approx. 280 μm. On the polished face of the GaAssubstrate 1, AuGe/Au is deposited and heattreated to form an n-typeelectrode 14.

A response characteristic of thus-manufactured semiconductor lightemitting device was examined, and the result of the examinationindicated that the rise time was 2.1 ns. In contrast, the rise time was2.6 ns in the case where the carrier density of the AlGaInP etchingprotection layer 29 was set to conventional 3×10¹⁸ cm⁻³. The examinationresult confirms that the response characteristic of the semiconductorlight emitting device was improved by decreasing the carrier density ofthe GaP etching protection layer 9.

Electric current diffusing outside of the current flow pass of the GaPcurrent constriction layer 10 is examined when resistivity of theetching protection layer 9 is changed. FIG. 4 is a graph showingexamined results thereof. In FIG. 4, the horizontal axis indicatesresistivity (Ωcm) of the etching protection layer 9, whereas thevertical axis indicates percentage (%) of current diffused to theoutside of the current flow pass with respect to the total appliedcurrent. Thickness of the etching protection layer 9 is 1 μm in all thecases.

As shown in FIG. 4, as the resistivity of the etching protection layer 9becomes larger, the percentage of the current diffused to the outside ofthe current flow pass becomes smaller.

Changes in rise time of the semiconductor light emitting device aremeasured when resistivity or the etching protection layer 9 is changed.FIG. 5 is a graph showing measured results thereof. In FIG. 5, thehorizontal axis indicates resistivity (Ωcm) of the etching protectionlayer 9, whereas the vertical axis indicates rise time (ns) that is atime elapsed from application of operating voltage to emission of light.Thickness of the etching protection layer 9 is 1 μm in all the cases.

As shown in FIG. 5, as the resistivity becomes smaller than 0.1 Ωcm, therise time rapidly becomes large. In this case, a value calculated bydividing the resistivity 0.1 Ωcm by the layer thickness 1 is equal to1×10³ Ω. More specifically, when the value obtained by dividingresistivity by layer thickness becomes smaller than 1×10³ Ω, the risetime of the semiconductor light emitting device rapidly increases. Thisis because a region of low current density in the light emission layerincreases by increase of the current diffused to the outside of thecurrent flow pass. More specifically, a response time to application ofcurrent with regard to light emission is long in the region of lowcurrent density, which brings about remarkable delay of the responsespeed of the entire semiconductor light emitting device. As shown inFIGS. 4 and 5, when the current diffused to the outside of the currentflow pass exceeds 25% of the total applied current, delay in rise timeof the entire semiconductor light emitting device becomes remarkable.Therefore, by restraining the current diffused outside the current flowpass to 25% or less with respect to the entire, applied current, itbecomes possible to effectively prevent the rise time of thesemiconductor light emitting device from delaying.

The p-type intermediate layer 8 has resistivity as large as approx. 0.3Ωcm, and has a layer thickness smaller than the etching protection layer9. Therefore, the p-type intermediate layer 8 hardly affects currentdiffusion from the current flow pass.

A current passing test of the semiconductor light emitting device of thepresent invention was carried out by applying SOmA current in anatmosphere where the temperature was 80° C. and the humidity was 85%. Asa result of the test, a optical output after the lapse of 1000 hours was95% of the initial optical output, which proved that the semiconductorlight emitting device was sufficiently proof against humidity. Theinitial optical output was 2.2 mW when applied current was 20 mA. Theoperating voltage when the applied current was 20 mA was 2.2V. Thisenables the current from the p-type electrode 13 to sufficiently diffuseinto the current diffusion layer 12 and to reach the center of thecircular opening on the current constriction layer 10. Thereby, thecurrent is uniformly applied to the current flow pass formed by thiscircular opening. As a result, current may be uniformly applied withhigh current density to the quantum well active layer 5 as a lightemission layer, which enables a semiconductor light emitting device tooperate in a low voltage with high speed response.

In the present embodiment, the p-type GaP etching protection layer 9 isformed between the second DBR 7 and the current constriction layer 10,where a value obtained by dividing resistivity with layer thickness islarger than 1×10³ Ω. However, any semiconductor layer other than theetching protection layer may be used as long as the layer be positionedbetween the second multilayered reflection film and the currentconstriction layer. For a material of this semiconductor layer,Al_(x)Ga_(1-x)As (0≦x≦1) is also usable. However, since this layer isrequired to be transparent against an emission wavelength, an Al mixcrystal ratio in the AlGaAs layer needs to be increased as the emissionwavelength becomes shorter. When the Al mix crystal ratio is increased,the layer surface is easily oxidized. Thereby, a layer laminated on thislayer is deteriorated in crystallinity. Therefore, a layer between thesecond multilayered reflection film and the current constriction layeris preferably formed by Al_(y)Ga_(z)In_(1-y-z)P (0 ≦y≦1, 0≦z≦1) when anemission wavelength of the semiconductor light emitting device is short.Although GaP is used for the current constriction layer in thisembodiment, AlGaAs (0≦x≦1) may also be used as a material of this layer.However, the layer is preferably transparent against any emissionwavelengths. When a layer between the second multilayered reflectionfilm and the current constriction layer is Al_(y)Ga_(z)In_(1-y-z)P,(0≦y≦1, 0≦z≦1), it is more difficult to secure crystallirity of thelaminated layer in the case of using AlGaAs for the current constrictionlayer because another layer should be laminated on a layer havingdifferent elements P, As belonging to V-group. Also, althoughAl_(0.01)Ga_(0.98)In_(0.01)P is used for the current diffusion layer inthis embodiment, Al_(x)Ga_(1-x)As (0≦x≦1) may be used as a material ofthis layer. However, since the layer needs to be transparent against anemission wavelength, Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1, 0 ≦z≦1) ispreferably used when the emission wavelength is short.Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1, 0≦z≦1) is small in Al mix crystal ratioand high in moisture resistance. Also, it is possible to do without theAlGaInP intermediate layer 8.

FIG. 6A is a plane view showing a semiconductor light emitting devicc ina second embodiment of the present invention. FIG. 6B is a crosssectional view taken along line C—C of FIG. 6A. FIG. 7 is a crosssectional view showing the state of the semiconductor light emittingdevice of FIGS. 6A and 6B in a manufacturing process. FIG. 8A is a planeview showing the state of the semiconductor light emitting device ofFIGS. 6A and 68 in a manufacturing process different from that of FIG.7. FIG. 8B is a cross sectional view taken along line D—D of FIG. 8A.

The semiconductor light emitting device of the present invention is aAlGaInP based semiconductor light emitting device. On an n-type GaAssubstrate 21 inclined 15° in [011] direction from (100) plane, there arelaminated in sequence by MOCVD method, as shown in FIG. 7, an n-typeGays buffer layer 22 (layer thickness of 1 μm, and carrier density of5×10¹⁷ cm⁻³) an n-type first DBR 23 (carrier density of 5×10¹⁷ cm⁻³), ann-type Al_(0.5)In_(0.5)P first cladding layer 24 (carrier density of5×10¹⁷ cm⁻³), a quantum well active layer 25, a p-type Al_(0.5)In_(0.5)Psecond cladding layer 26 (carrier density of 5×10¹⁷ cm⁻³), a p-typesecond DBR 27 (carrier density of 5×10¹⁷ cm⁻³), a p-type AlGaInPintermediate layer 28 (layer thickness of 0.1 μm, and carrier density of5×10¹⁸ cm⁻³), a p-type Al_(0.01)Ga_(0.98)In_(0.01)P etching protectionlayer 29 (layer thickness of 1μm, and carrier density of 1×10³⁹ cm⁻³),an n-type Al_(0.01)Ga_(0.98)In_(0.01)P current constriction layer 30(layer thickness of 0.3 μm, and carrier density of 3×10¹⁸ cm⁻³), and anundope GaAs cap layer 31 with a thickness of 0.01 μm.

The n-type first DBR 23 is formed by 35.5 pairs of n-type AlAs andn-type Al_(0.6)Ga_(0.4)As. The quantum well active layer 25 is formed bya (Al_(0.3)Ga_(0.7))_(0.5)In_(0.5)P well layer and an(Al_(0.7)Ga_(0.3))_(0.5)P barrier layer. The p-type second DBR is formedby 17 pairs of p-type (Al_(0.4)Ga_(0.6))_(0.5)In_(0.5)P and p-typeAl_(0.5)In_(0.5)P.

Herein, the n-type first DBR 23 and the p-type second DBR 27 are formedsuch that a center of each reflectance spectrum is 570 nm. An intervalbetween the DBRs 23 and 27, that is, a resonator length is adjusted sothat a resonance wavelength of a resonator becomes 570 nm, the resonatorbeing composed of these two DBRs 23, 27. In the present embodiment, theresonator length is set to be equal to two wavelengths. Further, thequantum well active layer 25 is positioned at an antinode of a standingwave generated in the resonator composed of the above two DBRs 23, 27,and to have an emission peak wavelength of 570 nm.

Then, after the n-type GaAs cap layer 31 is removed with sulfuricacid/hydrogen peroxide etchant, part of the n-typeAl_(0.01)Ga_(0.98)In_(0.01)P current constriction layer 30 is etched offtill the p-type Al_(0.01)Ga_(0.98)In_(0.01)P etching protection layer 29is exposed by using photo lithography and sulfuric acid/hydrogenperoxide etchant. As shown in FIGS. 8A and 8B, this etching processforms a circular opening of 70 μm in diameter, which functions as acurrent flow pass, so as to form the n-type Al_(0.01)Ga_(0.98)In_(0.01)Pcurrent constriction layer 30.

Thereafter, as shown in FIG. 6, a p-type AlGaInP current diffusion layer32 is laminated on the n-type current constriction layer 30 and thep-type etching protection layer 29. The p-type current diffusion layer32 is formed such that a total layer thickness is 7 μm. A lower 1μm-thick portion has a carrier density of 1×10¹⁸ cm⁻³ while an upper 6μm-thick portion has a carrier density of 1×10¹⁹ cm⁻³. Then, AuBe/Au isdeposited on the p-type current diffusion layer 32. The depositedAuBe/Au is etched by Au etchant after photo lithography, and thenheat-treated to obtain a p-type electrode 33. Meanwhile, the back faceof the GaAs substrate 21 is polished to have a thickness of approx. 280μm. AuGe/Au is deposited on the polished face of the GaAs substrate, andis heat-treated to form an n-type electrode 34.

A response characteristic of thus-manufactured semiconductor lightemitting device was examined, and the result of the examinationindicated that the rise time was 1.8 ns. In contrast, the rise time was2.5 ns in the case where the carrier density of the AlGaInP etchingprotection layer 29 was set to conventional 3×10¹⁸ cm⁻³. The examinationresult confirms that the response characteristic of the semiconductorlight emitting device was improved by decreasing the carrier density ofthe AlGaInP etching protection layer 29.

The semiconductor light emitting device of the present embodiment isdifferent from the first embodiment in the point that the etchingprotection layer 29 is formed by Al_(0.01)Ga_(0.98)In_(0.01)P. Whencompared with the GaP etching protection layer 9 of the semiconductorlight emitting device in the first embodiment, the resistivity thereofincreases byseveral % in the same carrier density since Al and In arerespectively contained by 1% in the present embodiment. Therefore,increased resistivity makes it possible to restrain a percentage of thecurrent diffused to the outside of the current flow pass to the lowlevel even if the layer thickness of the etching protection layer isincremented.

A current passing test of the semiconductor light emitting device of thepresent invention was carried out with applied current of 50 mA in anatmosphere where the temperature was 80° C. and the humidity was 85%. Asa result of the test, a percentage of optical output after the lapse of1000 hours was 105% of the initial optical output, which proved that thesemiconductor light emitting device was sufficient proof againsthumidity. The initial optical output was 0.4 mW when applied current was20 mA. Further, the operating voltage was 2.2V when the applied currentwas 20 mA. As with the first embodiment, the current is uniformlyapplied to the current flow pass which is formed by this circularopening. This is achieved by sufficiently diffusing the current from thep-type electrode 33 into the current diffusion layer 32, to reach thecenter of the circular opening on the current constriction layer 30. Asa result, the current is uniformly applied to the quantum well activelayer 25 in high current density. Thus, a semiconductor light emittingdevice having high speed response and operating in a low voltage can beobtained.

In the present embodiment, the p-type AlGaInP etching protection layer29 is formed between the second DBR 27 and the current constrictionlayer 30, and a value obtained by dividing resistivity by layerthickness is larger than 1×10³ Ω. However, any semiconductor layer otherthan the etching protection layer may be used as long as thesemiconductor layer be positioned between the second multilayeredreflection film and the current constriction layer. Also, it is possibleto do without the AlGaInP intermediate layer 28.

In the semiconductor light emitting device of the first or secondembodiment, p type and n type may be reversely used.

As mentioned above, the semiconductor light emitting device of thepresent embodiments is provided with a resonator that is formed by afirst multilayered reflection film on the side of a semiconductorsubstrate and a second multilayered reflection film on the side far fromthe semiconductor substrate. The second multilayered reflection film ismade of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1, 0≦z≦1). Also, the semiconductorlight emitting device is provided with a semiconductor layer locatedbetween the second multilayered reflection film and a currentconstriction layer, the semiconductor layer having a value calculated bydividing resistivity by thickness being 1×10³ Ω or more. This makes itdifficult to diffuse a current from a current flow pass, which is formedin the current constriction layer, to the outside of the current flowpass. Thereby, a region of low current density is hardly generated inthe light emission layer. As a result, it becomes possible toeffectively improve the response characteristic of the semiconductorlight emitting device.

In the semiconductor light emitting device according to the presentinvention, a current diffused to the outside of the current flow passformed in the current constriction layer is 25% or less of the totalcurrent applied to the current flow pass. This makes it possible todecrease generation of the low current density region in the lightemission layer, bad influence is hardly posed on the responsecharacteristic of the entire semiconductor light emitting device.

The invention being thus described, it will be obvious that theinvention may be varied in many ways. Such variations are not beregarded as a departure from the spirit and scope of the invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. A semiconductor light emitting device comprising:a semiconductor substrate; a first multilayered reflection film on thesemiconductor substrate; a light emission layer on the firstmultilayered reflection film; a second multilayered reflection film madeof Al_(y)Ga_(z)In_(1-y-z)P, wherein 0≦y≦1 and 0≦z≦1, on the lightemission layer; a semiconductor layer on the second multilayeredreflection film; and a current constriction layer on the semiconductorlayer, wherein the first multilayered reflection film and the secondmultilayered reflection film form a resonator with a specified interval,and the light emission layer is formed in a position of an antinode of astanding wave inside the resonator, and wherein the semiconductor layerhas a value obtained by dividing resistivity by thickness being 1×10³ Ωor more.
 2. The semiconductor light emitting device as defined in claim1, further comprising a current diffusion layer on the currentconstriction layer.
 3. The semiconductor light emitting device asdefined in claim 1, wherein the semiconductor substrate is made of GaAs,the light emission layer is made of Al_(y)Ga_(z)In_(1-y-z)P, wherein0≦y≦1 and 0≦z≦1, and the semiconductor layer is made ofAl_(y)Ga_(z)In_(1-y-z)P, wherein 0≦y≦1 and 0≦z≦1, or GaP.
 4. Thesemiconductor light emitting device as defined in claim 1, wherein thesemiconductor substrate is made of GaAs, the semiconductor layer is madeof Al_(y)Ga_(z)In_(1-y-z)P (O≦y≦1, 0≦z≦1) or GaP, and the currentconstriction layer is made of Al_(y)Ga_(z)In_(1-y-z)P, wherein 0≦y≦1 and0≦z ≦1, or GaP.
 5. The semiconductor light emitting device as defined inclaim 1, wherein the semiconductor substrate is made of GaAs, thesemiconductor layer is made of Al_(y)Ga_(z)In_(1-y-z)P, wherein 0≦y≦1and 0≦z≦1, or GaP, a current diffusion layer is provided on the currentconstriction layer, and is made of Al_(y)Ga_(z)In_(1-y-z)P, wherein0≦y≦1 and 0≦z≦1.
 6. A semiconductor light emitting device comprising: asemiconductor substrate; a first multilayered reflection film on thesemiconductor substrate; a light emission layer on the firstmultilayered reflection film; a second multilayered reflection film madeof Al_(y)Ga_(z)In_(1-y-z)P, wherein 0≦y≦1 and 0≦z≦1, on the lightemission layer; a semiconductor layer on the second multilayeredreflection film said semiconductor layer having a carrier density; and acurrent constriction layer on the semiconductor layer, wherein the firstmultilayered reflection film and the second multilayered reflection filmform a resonator with a specified interval, and the light emission layeris formed in a position of an antinode of a standing wave inside theresonator, and wherein said carrier density of the semiconductor layeris set such that a percentage of a current diffused to an outside of acurrent flow pass formed in the current constriction layer is 25% orless of a total current applied to the current flow pass.
 7. A Thesemiconductor light emitting device as defined in claim 6, furthercomprising a current diffusion layer on the current constriction layer.8. The semiconductor light emitting device as defined in claim 6,wherein the semiconductor substrate is made of GaAs, the light emissionlayer is made of Al_(y)Ga_(z)In_(1-y-z)P, wherein 0≦y≦1 and 0≦z≦1, andthe semiconductor layer is made of Al_(y)Ga_(z)In_(1-y-z)P wherein 0≦y≦1and 0≦z≦1, or GaP.
 9. The semiconductor light eniitting device asdefined in claim 6, wherein the semiconductor substrate is made of GaAs,the semiconductor layer is made of Al_(y)Ga_(z)In_(1-y-z)P, wherein0≦y≦1 and 0≦z≦1, or GaP, and the current constriction layer is made ofAl_(y)Ga_(z)In_(1-y-z) P, wherein 0≦y≦1 and 0≦z ≦1, or GaP.
 10. Thesemiconductor light emitting device as defined in claim 6, wherein thesemiconductor substrate is made of GaAs, the semiconductor layer is madeof Al_(y)Ga_(z)In_(1-y-z)P, wherein 0≦y≦1 and 0≦z≦1, or GaP, a currentdiffusion layer is provided on the current constriction layer, and thecurrent diffusion layer is made of Al_(y)Ga_(z)In_(1-y-z)P, wherein0≦y≦1 and 0≦z≦1.
 11. The semiconductor light emitting device as definedin claim 6, wherein the carrier density is 1×10¹⁸ cm⁻³.